Aluminium/magnesium (AlMg) alloys of the type 5xxx are used in the form of sheets or plates or strips for the construction of welded or joined structures, in ship, automotive and aircraft construction. They are distinguished by a particularly high level of strength, the levels of strength of the AlMg alloys increasing as the magnesium content increases. Typical representatives of aluminium alloys of the type 5xxx are, for example, the aluminium alloys of the type AA 5049, AA 5454 or AA 5918. The alloys are AlMg2Mn (5049)—AlMg3Mn (5454)—or AlMg3.5Mn (5918) aluminium alloys. The constant requirement for additional reduction of weight requires aluminium alloys with higher levels of strength and consequently with correspondingly higher magnesium (Mg) contents in order to provide the desired levels of strength. The problem with AlMgMn aluminium alloys with Mg contents of more than 2.4% by weight is that they have an increased tendency towards intercrystalline corrosion when they are subjected to high temperatures for longer periods of time. It has been found that in AlMgMn aluminium alloys with more than 2.4% by weight of magnesium, at temperatures of from 70 to 200° C., β-Al5Mg3 phases are precipitated along the grain boundaries. When the grain boundaries are continuously occupied with β particles and when a corrosive medium is present, the dissolution of these β phases may lead to a selective corrosion attack along the grain boundaries. Consequently, this leads to aluminium alloys with increased Mg contents either not being able to be used in thermally loaded regions or having to have reduced Mg contents as a result of the heat development so that the precipitation of β-Al5Mg3 particles is minimised and a continuous occupation of the grain boundaries with β-Al5Mg3 particles is excluded. Proposals for a solution to this problem have already been set out in the prior art. For example, the German Patent Application DE 102 31 437 A1 proposes significantly reducing the susceptibility with respect to intercrystalline corrosion by means of a specific aluminium alloy composition, even after sensitisation as a result of heat. To this end, it proposes the following aluminium alloy composition:                3.1%<Mg<4.5%,        0.4%<Mn<0.85%,        0.4%<Zn<0.8%,        0.06%<Cu<0.35%,                    Cr<0.25%,            Fe<0.35%,            Si<0.2%,            Zr<0.25%,            Ti<0.3%,impurities of ≤0.05% in each case and a total of a maximum of 0.15%, balance aluminium.                        
However, it has been found that the results with respect to the susceptibility to intercrystalline corrosion, which is measured and evaluated in accordance with the Standard ASTM G67, are capable of improvement. Furthermore, the aluminium alloy permits a content of up to 0.25% of zirconium, which is considered to be critical with respect to the recycling of the aluminium alloy. From the international Patent Application WO 99/42627, there is further known a zirconium-containing aluminium alloy which, although it achieved very good results in the ASTM G67 test, is problematic to use owing to the zirconium content which is necessarily present.